Inspiratory time, pressure settings, and site of supplemental oxygen insertion affect delivered oxygen fraction with the quantum PSV noninvasive positive pressure ventilator

BACKGROUND: With noninvasive positive pressure ventilation (NPPV), the fraction of delivered oxygen (F(DO₂)) can change if other ventilatory parameters are altered, but the extent and precise nature of the relationship between F(DO₂), and other ventilatory parameters is not well understood. METHODS: We studied a new NPPV device, the Quantum PSV (Respironics Inc, Marietta, Georgia) to measure changes in the F(DO₂) with changes in 4 ventilatory parameters: (1) inspiratory pressure, (2) expiratory pressure, (3) inspiratory time fraction (T₁), and (4) insertion point of supplemental oxygen. RESULTS: Each oxygen L/min increase yielded a 0.05-0.06 increase in the oxygen concentration delivered to the test lung. Changing the site of oxygen introduction resulted in a 0.04-0.10 increase in mean F(DO₂). Comparing mean F(DO₂) values from both oxygen introduction sites yielded p- values < 0.001 for each level of O₂ flow. Oxygen at CPAP levels of 4 and 10 cm H₂O produced mean F(DO₂) values of 0.71 and 0.48 respectively at 10 L/min O₂, and 0.98 and 0.70 at 15 L/min O₂. When data from all 4 inspiratory positive airway pressure-expiratory positive airway pressure (IPAP-EPAP) combinations were pooled, F(DO₂) was significantly higher with T₁ = 0.25 than with T₁ = 0.35 (p < 0.001). Within each IPAP-EPAP level (10 and 15 cm H₂O), all 3 pairs were different, yielding p-values < 0.001. CONCLUSIONS: Altering T₁ and EPAP level (while maintaining a constant pressure gradient) both significantly changed F(DO₂). Introducing oxygen into the patient circuit at the point most distant from the patient (nearest to the ventilator) provided higher F(DO₂) values than when oxygen was inserted near the mask, but adding oxygen at the distal site is not advisable in that it might increase fire hazard. Clinicians should be aware that during NPPV, changing ventilator control settings can significantly alter F(DO₂).